then you can't have abortion either, and not only that but you got to go and rally against abortions. While you're at it, against contraceptives also.

Let's assume you're a total hedonistic utilitarian: you want to maximize happiness over all people over all time. Naively, yes, abortions and contraception would decrease total all-time happiness because they decrease the number of future people. But prohibiting abortions and contraception also has negative effects on other people; lots of people get pregnant and really don't want to have a baby. When abortion is illegal you have back-alley abortions which have a high chance of killing the woman. Even if we assume that the harm of requiring people to go through with unwanted pregnancies is minor and that no women will get abortions anyway, there's still the question of whether an additional person will increase total happiness. It's possible that the happiness of that particular extra person would be less than the distributed unhappiness caused by adding another person to a highly populated world.

Whether abortions or contraception prohibition is good public policy depends on its effects, which are not entirely known. They look negative to me, but I'm not that sure. We can increase our chances of making the right choice with more research, but I don't see this as understood enough for pro-life or pro-choice advocacy to be a good use of my time.

Got an action, pick an utilitarianism, pick a good sounding utility, and you have yourself a very noble goal towards which your decision works.

This isn't how to use a moral system. Any moral system can be abused if you're acting in bad faith.